The function in a digital television of downloading a program and checking/guaranteeing the credibility of such program is described in the DVB-MHP specification “ETSI TS 101 812 V1.2.1 DVB-MHP Specification 1.0.2”, and others. This DVB-MHP specification defines the function of verifying that a program superimposed on a broadcast wave being received has not been tampered with as well as that whether or not such program was issued by a reliable organization. This function makes it possible to prevent a rewritten program that dose not operate as originally required and therefore would inflict damage to the digital television and a program of a spoofing third party, from being activated.
In addition, the Japanese Laid-Out Patent Application No. 2000-29833 describes a technique, which is comprised of a server apparatus for accumulating and transmitting data and a terminal apparatus for receiving data via a network, to prevent accumulated data from being illicitly used by accumulating the received data in the terminal apparatus. FIG. 1 of the Japanese Laid-Out Patent Application No. 2000-29833 illustrates the technique that the server apparatus 10 copies data stored in the storage unit 15 into the storage unit 23 in response to a request from the terminal apparatus 20, and when the data stored in the storage unit 23 is wished to be used, the inquiry unit 26 makes an inquiry to the server apparatus 10, the authentication unit 13 performs an audit about the use of the data, and if there is no problem, the terminal apparatus 20 uses the data. The above apparatus is capable of loading data after checking the credibility of the data stored in a non-volatile memory even when the power is turned ON/OFF. Checking the credibility of programs and data is hereinafter referred to as authentication.
According to a conventional technique, however, in the case of storing a program into a non-volatile memory once so as to activate such program after the apparatus is powered ON/OFF, authentication of the program is performed immediately before it is activated. In this case, it is necessary to perform calculations such as decryption of an encrypted value before the activation of the program starts, which causes a problem that responsiveness is decreased more as a longer time is required for calculations. Especially in the case where a program is frequently activated or where the capacity of a program is large, the responsiveness becomes more and more degraded since the amount of calculations increases in proportion to activation frequency and capacity.
In view of the above problem, it is desired to provide a program authentication apparatus such as digital television with increased responsiveness that is capable of shortening the time required before a program is activated, while guaranteeing the credibility of the program.